The present invention relates generally to broadband amplifiers and communication systems, and more particularly to broadband booster amplifiers and communication systems with Raman and rare-earth doped amplifiers.
2. Description of Related Art
Because of the increase in data intensive applications, the demand for bandwidth in communications has been growing tremendously. In response, the installed capacity of telecommunication systems has been increasing by an order of magnitude every three to four years since the mid 1970s. Much of this capacity increase has been supplied by optical fibers that provide a four-order-of-magnitude bandwidth enhancement over twisted-pair copper wires.
To exploit the bandwidth of optical fibers optical amplifiers and wavelength-division multiplexing (WDM) have been developed and utilized in optical communications. Optical amplifiers boost the signal strength and compensate for inherent fiber loss and other splitting and insertion losses. WDM enables different wavelengths of light to carry different signals parallel over the same optical fiber. Although WDM is critical in that it allows utilization of a major fraction of the fiber bandwidth, it would not be cost-effective without optical amplifiers. In particular, a broadband optical amplifier that permits simultaneous amplification of many WDM channels is a key enabler for utilizing the full fiber bandwidth.
Silica-based optical fiber has its lowest loss window around 1550 nm with approximately 25 THz of bandwidth between 1430 and 1620 mn. In this wavelength region, erbium-doped fiber amplifiers (EDFAs) are widely used. However, the absorption band of a EDFA nearly overlaps its the emission band. For wavelengths shorter than about 1525 nm, erbium-atoms in typical glasses will absorb more than amplify. To broaden the gain spectra of EDFAs, various dopings have been added. Co-doping of the silica core with aluminum or phosphorus broadens the emission spectrum considerably. Nevertheless, the absorption peak for the various glasses is still around 1530 nm.
Broadening the bandwidth of EDFAs to accommodate a larger number of WDM channels has become a subject of intense research. A two-band architecture for an ultra-wideband EDFA has been developed with an optical bandwidth of 80 nm. To obtain a low noise figure and high output power, the two bands share a common first gain section and have distinct second gain sections. The 80 nm bandwidth comes from one amplifier (so-called conventional band or C-band) from 1525.6 to 1562.5 nm and another amplifier (so-called long band or L-band) from 1569.4 to 1612.8 nm.
These recent developments illustrate several points in the search for broader bandwidth amplifiers for the low-loss window in optical fibers. First, even with EDFAs, bandwidth in excess of 40-50 nm requires the use of parallel combination of amplifiers. Second, the 80 nm bandwidth may be very close to the theoretical maximum. The short wavelength side at about 1525 nm is limited by the inherent absorption in erbium, and long wavelength side is limited by bend-induced losses in standard fibers at above 1620nm. Therefore, even with these recent advances, half of the bandwidth of the low-loss window, i.e., 1430-1530 nm, remains without an optical amplifier.
There is a need for a broadband amplifier and broadband communication system suitable for a wide range of wavelengths.
Accordingly an object of the present invention is to provide broadband amplifiers and communication systems.
Another object of the present invention is to provide broadband amplifiers and communication systems that are suitable for use.
Another object of the present invention is to provide broadband amplifiers and communication systems that include Raman and rare-earth doped amplifiers.
Yet another object of the present invention is to provide broadband amplifiers and communication systems that are suitable for use for WDM wavelengths of 1430 to 1530 nm. A further object of the present invention is to provide broadband amplifiers and communication systems that are suitable for use for WDM wavelengths of 1430 to 1530 nm in combination with wavelengths of 1530 to 1620 nm.
Another object of the present invention to provide a parallel optical amplification apparatus and communication system that includes Raman and rare-earth doped optical amplifiers.
Still another object of the present invention to provide a parallel optical amplification apparatus and communication system that includes Raman and rare-earth doped optical amplifiers and a splitter with a transition from a stop band to a pass band in 20 nm or less.
Yet another object of the present invention to provide a parallel optical amplification apparatus and communication system that includes Raman and rare-earth doped optical amplifiers and a combiner with a transition from a stop band to a pass band in 20 nm or less.
These and other objects of the present invention are achieved in an in-line broadband amplifier. The amplifier includes at least one input fiber and a WDM splitter coupled to the input fiber. The splitter splits an optical signal into at least a first wavelength and a second wavelength. A transition from a stop band to a pass band of the splitter occurs in 20 nm or less. A Raman amplifier and a rare-earth doped optical amplifier are coupled to the splitter. A WDM combiner is coupled to the Raman amplifier and the rare-earth doped optical amplifier. The WDM combiner combines an optical signal into at least a first wavelength and a second wavelength. A transition from a stop band to a pass band of the combiner occurs in 20 nm or less. An output fiber is coupled to the WDM combiner.
In another embodiment of the present invention, a broadband booster amplifier includes a plurality of transmitters that emit a plurality of wavelengths. At least a first band of wavelengths and a second band of wavelengths are produced. A Raman amplifier is coupled to at least a portion of the plurality of transmitters and amplifies the first band of wavelengths. A rare-earth doped optical amplifier is coupled to at least a portion of the plurality of transmitters and amplifies the second band of wavelengths. A WDM combiner is coupled to the Raman amplifier and the rare-earth doped optical amplifier. The WDM combiner combines an optical signal into at least a first wavelength and a second wavelength. A transition from a stop band to a pass band of the combiner occurs in 20 nm or less. An output fiber is coupled to the WDM combiner.
In another embodiment of the present invention, a broadband communication system includes a transmitter and at least one input fiber coupled to the transmitter. A WDM splitter is coupled to the input fiber. The splitter splits an optical signal into at least a first wavelength and a second wavelength. A Raman amplifier and a rare-earth doped optical amplifier are coupled to the splitter. A WDM combiner is coupled to the Raman amplifier and the rare-earth doped optical amplifier. The WDM combiner combines an optical signal into at least a first wavelength and a second wavelength. An output fiber is coupled to the WDM combiner. At least one in-line broadband amplifier is coupled to the output fiber. A receiver is coupled to the in-line amplifier.
In another embodiment of the present invention, a broadband communication system, includes a transmitter and at least one input fiber coupled to the transmitter. A WDM splitter is coupled to the input fiber. The splitter splits an optical signal into at least a first beam and a second beam. A transition from a stop band to a pass band of the coupler occurs in 15 nm or less. A Raman amplifier coupled to the splitter and a rare-earth doped optical amplifier are coupled to the splitter. A WDM combiner is coupled to the Raman amplifier and the rare-earth doped optical amplifier. An output fiber is coupled to the WDM combiner and a broadband pre-amplifier is coupled to the output fiber.
In another embodiment of the present invention, a broadband communication system, includes a transmitter and a booster broadband amplifier coupled to the transmitter. At least one input fiber is coupled to booster amplifier. A WDM splitter is coupled to the input fiber. A Raman amplifier and a rare-earth doped optical amplifier are coupled to the splitter. A WDM combiner is coupled to the Raman amplifier and the rare-earth doped optical amplifier. An output fiber is coupled to the WDM combiner and a broadband pre-amplifier is coupled to the output fiber. A receiver is coupled to the broadband pre-amplifier.